Lamp containing fixed reverse phase switching power supply with time-based phase pulse triggering control

ABSTRACT

A lamp contains a lamp voltage conversion circuit within the lamp and connected to a lamp terminal. The voltage conversion circuit includes a phase-control clipping circuit that clips a load voltage and provides an RMS load voltage to the lamp. The phase-control clipping circuit has a time-based pulse source that triggers conduction of the phase-control clipping circuit independently of line voltage magnitude.

BACKGROUND OF THE INVENTION

The present invention is directed to a power controller that supplies aspecified power to a load, and more particularly to a voltage converterfor a lamp that converts line voltage to a voltage suitable for lampoperation.

Some loads, such as lamps, operate at a voltage lower than a line (ormains) voltage of, for example, 120V or 220V, and for such loads avoltage converter that converts line voltage to a lower operatingvoltage must be provided. The power supplied to the load may becontrolled with a phase-control clipping circuit that typically includesan RC circuit. Moreover, some loads operate most efficiently when thepower is constant (or substantially so). However, line voltagevariations are magnified by these phase-control circuits due to theirinherent properties (as will be explained below) and the phase-controlcircuit is desirably modified to provide a (more nearly) constant RMSload voltage.

A simple four-component RC phase-control clipping circuit demonstrates aproblem of conventional phase-control clipping circuits. Thephase-controlled clipping circuit shown in FIG. 1 has a capacitor 22, adiac 24, a triac 26 that is triggered by the diac 24, and resistor 28.The resistor 28 may be a potentiometer that sets a resistance in thecircuit to control a phase at which the triac 26 fires.

In operation, a clipping circuit such as shown in FIG. 1 has two states.In the first state the diac 24 and triac 26 operate in the cutoff regionwhere virtually no current flows. Since the diac and triac function asopen circuits in this state, the result is an RC series network such asillustrated in FIG. 2. Due to the nature of such an RC series network,the voltage across the capacitor 22 leads the line voltage by a phaseangle that is determined by the resistance and capacitance in the RCseries network. The magnitude of the capacitor voltage V_(C) is alsodependent on these values.

The voltage across the diac 24 is analogous to the voltage drop acrossthe capacitor 22 and thus the diac will fire once breakover voltageV_(BO) is achieved across the capacitor. The triac 26 fires when thediac 24 fires. Once the diac has triggered the triac, the triac willcontinue to operate in saturation until the diac voltage approacheszero. That is, the triac will continue to conduct until the line voltagenears zero crossing. The virtual short circuit provided by the triacbecomes the second state of the clipping circuit as illustrated in FIG.3.

Triggering of the triac 26 in the clipping circuit is forwardphase-controlled by the RC series network and the leading portion of theline voltage waveform is clipped until triggering occurs as illustratedin FIGS. 4-5. A load attached to the clipping circuit experiences thisclipping in both voltage and current due to the relatively largeresistance in the clipping circuit.

Accordingly, the RMS load voltage and current are determined by theresistance and capacitance values in the clipping circuit since thephase at which the clipping occurs is determined by the RC seriesnetwork and since the RMS voltage and current depend on how much energyis removed by the clipping.

With reference to FIG. 6, clipping is characterized by a conductionangle α and a delay angle θ. The conduction angle is the phase betweenthe point on the load voltage/current waveforms where the triac beginsconducting and the point on the load voltage/current waveform where thetriac stops conducting. Conversely, the delay angle is the phase delaybetween the leading line voltage zero crossing and the point where thetriac begins conducting.

Define V_(irrms) as RMS line voltage, V_(orms) as RMS load voltage, T asperiod, and ω as angular frequency (rad) with ω=2πf.

Line voltage may vary from location to location up to about 10% and thisvariation can cause a harmful variation in RMS load voltage in the load(e.g., a lamp). For example, if line voltage were above the standard forwhich the voltage conversion circuit was designed, the triac 26 maytrigger early thereby increasing RMS load voltage. In a halogenincandescent lamp, it is particularly desirable to have an RMS loadvoltage that is nearly constant.

Changes in the line voltage are exaggerated at the load due to avariable conduction angle, and conduction angle is dependent on the rateat which the capacitor voltage reaches the breakover voltage of thediac. For fixed values of frequency, resistance and capacitance, thecapacitor voltage phase angle (θ_(C)) is a constant defined byθ_(C)=arctan (−ωRC). Therefore, the phase of V_(C) is independent of theline voltage magnitude. However, the rate at which V_(C) reaches V_(BO)is a function of V_(irms) and is not independent of the line voltagemagnitude.

FIG. 7 depicts two possible sets of line voltage V_(i) and capacitorvoltage V_(C). As may be seen therein, the rate at which V_(C) reachesV_(BO) varies depending on V_(irrms). For RC phase-control clippingcircuits the point at which V_(C)=V_(BO) is of concern because this isthe point at which diac/triac triggering occurs. As V_(irrms) increases,V_(C) reaches V_(BO) earlier in the cycle leading to an increase inconduction angle (α₂>α₁), and as V_(irrms) decreases, V_(C) reachesV_(BO) later in the cycle leading to a decrease in conduction angle(α₂<α₁).

Changes in V_(irrms) leading to exaggerated or disproportional changesin V_(orms) are a direct result of the relationship between conductionangle and line voltage magnitude. As V_(irrms) increases, V_(orms)increases due to both the increase in peak voltage and the increase inconduction angle, and as V_(irrms) decreases, V_(orms) decreases due toboth the decrease in peak voltage and the decrease in conduction angle.Thus, load voltage is influenced twice, once by a change in peak voltageand once by a change in conduction angle, resulting in unstable RMS loadvoltage conversion for the simple phase-control clipping circuit.

When the phase-control power controller is used in a voltage converterof a lamp, the voltage converter may be provided in a fixture to whichthe lamp is connected or within the lamp itself. U.S. Pat. No. 3,869,631is an example of the latter, in which a diode is provided in the lampbase for clipping the line voltage to reduce RMS load voltage at thelight emitting element. U.S. Pat. No. 6,445,133 is another example ofthe latter, in which transformer circuits are provided in the lamp basefor reducing the load voltage at the light emitting element.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a novel phase-controlpower controller that converts a line voltage to an RMS load voltageindependently of variations in line voltage magnitude.

A further object is to provide a novel phase-control power controllerwith a phase-control clipping circuit that performs phase-controlclipping of a load voltage to provide an RMS load voltage, where aconduction angle of the phase-control clipping circuit is defined by atime-based pulse source that triggers conduction in the phase-controlclipping circuit independently of line voltage magnitude.

A yet further object is to provide a novel phase-control powercontroller with a fixed, reverse phase-control clipping circuit thatincludes a transistor switch whose gate receives positive polaritysignals from a time-based pulse source to trigger conduction of thephase-control clipping circuit.

A still further object is to provide a lamp with this power controllerin a voltage conversion circuit that converts a line voltage at a lampterminal to the RMS load voltage usable by a light emitting element ofthe lamp.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic circuit diagram of a phase-controlled clippingcircuit of the prior art.

FIG. 2 is a schematic circuit diagram of the phase-controlled dimmingcircuit of FIG. 1 showing an effective state in which the triac is notyet triggered.

FIG. 3 is a schematic circuit diagram of the phase-controlled dimmingcircuit of FIG. 1 showing an effective state in which the triac has beentriggered.

FIG. 4 is a graph illustrating current clipping in the phase-controlleddimming circuit of FIG. 1.

FIG. 5 is a graph illustrating voltage clipping in the phase-controlleddimming circuit of FIG. 1.

FIG. 6 is a graph showing the conduction angle α.

FIG. 7 is a graph showing how changes in the magnitude of the linevoltage affect the rate at which capacitor voltage reaches the diacbreakover voltage.

FIG. 8 is a partial cross section of an embodiment of a lamp of thepresent invention.

FIG. 9 is a schematic circuit diagram showing an embodiment of thefixed, reverse phase-control power controller of the present invention.

FIG. 10 is a graph depicting the reverse phase clipping of the presentinvention, including the unclipped and clipped load voltages.

FIG. 11 is a graph depicting the reverse phase clipping of the presentinvention, including the clipped load voltage and the pulse signal fromthe time-based signal source.

FIG. 12 is a graph of V_(orms) versus V_(irms) for a conventional RCphase-control power controller designed to produce 42 V_(rms) output for120 V_(rms) input.

FIG. 13 is a graph of V_(orms) versus V_(irms) for a fixed phase-controlpower controller incorporating the present invention and designed toproduce 42 V_(rms) output for 120 V_(rms) input.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to FIG. 8, a lamp 10 includes a base 12 with a lampterminal 14 that is adapted to be connected to line (mains) voltage, alight-transmitting envelope 16 attached to the base 12 and housing alight emitting element 18 (an incandescent filament in the embodiment ofFIG. 8), and a voltage conversion circuit 20 for converting a linevoltage at the lamp terminal 14 to a lower operating voltage. Thevoltage conversion circuit 20 may be within the base 12 and connectedbetween the lamp terminal 14 and the light emitting element 18. Thevoltage conversion circuit 20 may be an integrated circuit in a suitablepackage as shown schematically in FIG. 1.

While FIG. 8 shows the voltage conversion circuit 20 in a parabolicaluminized reflector (PAR) halogen lamp, the voltage conversion circuit20 may be used in any incandescent lamp when placed in series betweenthe light emitting element (e.g., filament) and a connection (e.g., lampterminal) to a line voltage. Further, the voltage conversion circuitdescribed and claimed herein finds application other than in lamps andis not limited to lamps.

With reference to FIG. 9 that illustrates an embodiment of the presentinvention, the voltage conversion circuit 20 includes line terminals 32for a line voltage and load terminals 34 for a load voltage, aphase-control clipping circuit 36 that clips the load voltage and thatis connected to the line and load terminals and has a transistor switch38 wherein a conduction angle of the phase-control clipping circuit 36determines an RMS load voltage, and a time-based signal source 40 thatsends signals at constant time intervals to a gate of the transistorswitch 38 that cause the transistor switch to be ON during time periodsthat define the conduction angle for the phase-control clipping circuit36.

In other words, the voltage conversion circuit includes a fixed, reversephase-control clipping circuit that clips a load voltage and provides anRMS load voltage to the lamp, where the phase-control clipping circuithas a time-based signal source that triggers conduction of thephase-control clipping circuit independently of line voltage magnitude.

Conventional RC phase-control clipping circuits are very sensitive tofluctuations in the line voltage magnitude. The present inventionprovides a power controller that operates substantially independently ofthe line voltage magnitude by incorporating time-based pulses to triggerconduction and thereby reduce the variation of the conduction anglecompared to conventional RC phase-control circuits. Additionally, thetime-based trigger makes it possible to use reverse phase-controlclipping by which the effects of electromagnetic interference (EMI) andtotal harmonic distortion (THD) are reduced in comparison to forwardphase-control clipping.

Reverse phase clipping is defined as clipping that removes power fromthe trailing edge of the cycle such as shown in FIG. 10, as opposed tothe forward clipping shown in FIGS. 4-5 that removes power from thefront of the cycle. The pulses sent to the transistor switch may be setto manipulate the switching to provide this reverse clipping.

In particular embodiments, the phase-control clipping circuit 36includes a full-wave bridge 42. In another embodiment the transistorswitch 38 is an insulated gate bipolar transistor. The time-based signalsource 40 may be any suitable signal source that sends signals atconstant time intervals to a gate of the transistor switch 38, includinga pulse generator, a microcontroller and a clock. The signals shouldhave a positive polarity at the gate of the transistor switch to providefixed, reverse phase-control clipping. Examples of waveforms of thepulse from the time-based signal source 40 and the reverse clipped loadvoltage are shown in FIG. 11.

In operation, the time-based signal source 40 generates positivepolarity pulses that are timed to coincide with the conduction region ofthe power controller. The time-based signal source 40 sustains thepulses for the entirety of each period the transistor switch 38 is to beconducting.

FIGS. 12 and 13 illustrate the improvement afforded by the presentinvention. FIG. 12 shows relationship between V_(orms) and V_(irms) in aprior art RC phase-control clipping circuit, while FIG. 13 shows therelationship for the fixed, reverse phase-control clipping circuit ofthe present invention. In each instance the circuit is designed toproduce 42 V_(rms) output for a 120 V_(rms) input. Note that the outputvoltage varies considerably more in FIG. 12 than in FIG. 13.

The description above refers to use of the present invention in a lamp.The invention is not limited to lamp applications, and may be used moregenerally where resistive or inductive loads (e.g., motor control) arepresent to convert an unregulated AC line or mains voltage at aparticular frequency or in a particular frequency range to a regulatedRMS load voltage of specified value.

While embodiments of the present invention have been described in theforegoing specification and drawings, it is to be understood that thepresent invention is defined by the following claims when read in lightof the specification and drawings.

1. A lamp comprising a lamp voltage conversion circuit within the lampand connected to a lamp terminal, said voltage conversion circuitincluding a phase-control clipping circuit that clips a load voltage andprovides an RMS load voltage to the lamp, said phase-control clippingcircuit having a time-based pulse source that triggers conduction ofsaid phase-control clipping circuit independently of line voltagemagnitude.
 2. The lamp of claim 1, wherein said time-based pulse sourceis one of a pulse generator, a microcontroller and a clock.
 3. The lampof claim 1, further comprising a base and a light-transmitting envelope,and wherein said voltage conversion circuit is within said base.
 4. Thelamp of claim 3, wherein said voltage conversion circuit is anintegrated circuit.
 5. The lamp of claim 1, wherein said phase-controlclipping circuit includes a transistor switch whose gate receivessignals from said time-based pulse source to trigger conduction of saidphase-control clipping circuit.
 6. The lamp of claim 5, wherein saidtransistor switch is an insulated gate bipolar transistor.
 7. The lampof claim 5, wherein the signals have a positive polarity at the gate ofsaid transistor switch.